Had a motor built a couple yrs ago.Started it 6mons later for about 5-6 mins.Smoked badly.Builder put oil in the cyls cause I told him it wasn;t gonna run right away.Oh well.A yr later I get the car together and start the motor for about 10 mins and smoking isn't as bad,but its still there.I took a couple header tubes off and inside the ports is a sticky blk residue.What might that be caused from? How long should it take to burn the cyl oil out?